This application is based on Japanese Patent Application No. Hei 11-60230.
1. Field of the Invention
The present invention relates to a heat exchanger arranged in an air conditioner for a vehicle or the like.
2. Description of the Related Arts
In a conventional heat exchanger in an air conditioner for a vehicle, a tube for a heat exchanger as shown in FIG. 10 has been used. This tube is manufactured by an extrusion process, then, a plurality of thin tubes are located inside the tube by forming a plurality of partitions 2 in a flat tube 1 when extruding.
Since a tube like the above is molded by extrusion, it is difficult to form the flat tube 1 and the partitions 2 so that they are thin, therefore, some problems have been observed, for example, a large amount of materials for the tube is required, therefore, production costs increase and the heat exchanging property cannot be improved because of the flat tube 1 and the partitions 2 have thick walls.
Recently, a tube for a heat exchanger to take the place of the above extruded tube, a tube such as shown in FIG. 11 has been proposed. A tubular portion 3 as this type of tube is formed by the steps of bending a flat plate in two, forming the upper and lower walls 4a and 4b roughly in parallel, overlapping the side edges of the upper and lower walls 4a and 4b, and brazing the overlapped side edges. The tubular portion 3 is characterized in that, since dimples (cavities) 5 are formed on the outer surfaces of the upper and lower walls 4a and 4b, the dimples 5 protrude inward when the dimples 5 are observed from the inside of the tubular portion 3 and a plurality of columns 6 are formed between the walls 4a and 4b by closely contacting the inner top of the dimple 5 formed on the either side wall to the inner top of the dimple 5 formed on the other side wall. By arranging the columns 6 in the tubular portion 3, turbulent flow occurs in the refrigerant which runs through the tubular portion 3. Therefore, its heat exchanging property is improved.
According to the dimple tube mentioned above, since the tubular portion is formed by bending a flat plate in two, the walls of the dimple tube can be thin. This provides several advantages, e.g., less material is used in the dimple tube, production costs decrease, and the heat exchanging property is improved. Furthermore, the columns 6 consisting of the dimples 5 are regularly arranged in the dimple tube along the length direction, so that a sufficient amount of pressure is obtained even if the thickness of the walls of the dimple tube are thin. This type of dimple tube will be introduced in air conditioners for vehicles in the future.
FIG. 12 shows a cross section of a part of the heat exchanger using the dimple tube. The ends of dimple tube 7 are inserted into a header 8 having a hollow cylindrical shape through a tube inserting hole 8a where they are joined by brazing.
One of the factors determining the heat exchanging property is pressure loss depending on rapid reduction and enlargement of the cross-sectional area of the refrigerant path when, for example, in the joint of the dimple tube 7 and the header 8 shown in FIG. 12, the refrigerant flows into the dimple tube 7 from the header 8 and the refrigerant flows into the header 8 from the dimple tube 7. This is because a plurality of dimples 5 are formed from one end to the other end of the dimple tube in a conventional dimple tube 7 and the columns 6 consisting of the dimples 5 reduce the opening area of the end of the dimple tube 7, so that the cross-sectional area of the refrigerant path is rapidly reduced or enlarged when the refrigerant flows through a joint of the dimple tube 7 and the header 8, therefore, pressure loss is increased.
In the light of the above, an object of the present invention is to provide a heat exchanger wherein rapid reduction and enlargement of the refrigerant path are prevented when the refrigerant flows at the joint of the dimple tube and the header and pressure loss of the refrigerant which flows into and out of the header to the tube is reduced.
To achieve the above object, the present invention provides a heat exchanger comprising a tube containing an upper wall and a lower wall arranged roughly in parallel, an overlap width, a path for a refrigerant, a plurality of protrusions protruding toward the path arranged on at least one of the inner surfaces of the upper and lower walls, and a plurality of columns formed by contacting the tops of the protrusions to the inner surface of the other wall and a header having a hollow cylindrical shape so that both ends of the tube are put into the header through a tube inserting hole and joined by brazing; wherein a flat tubular portion without the protrusions is provided at the end of the tube to be inserted into the header and the length of the flat tubular portion is 15 mm or less along the direction of the length of the tube.
Furthermore, the length of the flat tubular portion may be from 5 to 15 mm.
Moreover, the overlap width may have a cut portion.
In this heat exchanger, since the flat tubular portion without columns is provided at the end of the tube, the opening area of the end of the tube is not reduced thereby. Therefore, rapid reduction and enlargement of the refrigerant path are presented when the refrigerant flows through the vicinity of the joint of the tube and the header and pressure loss of the refrigerant which flows into and out of the header to the tube is reduced.
Furthermore, as to another aspect, the present invention provides a heat exchanger comprising: a tube containing an upper wall and a lower wall arranged roughly in parallel and consisting of a part of a path for a refrigerant, a plurality of protrusions protruding toward the path arranged on at least one of inner surfaces of the upper and lower walls, and a plurality of columns formed by contacting the tops of the protrusions to the inner surface of the other wall and a header having a hollow cylindrical shape in which both ends of the tubes are put into the header through a tube inserting hole and joined by brazing; wherein the tube includes a flared outer end portion and a guard or stop located intermediate the protrusions and the end portion and closing the tube inserting hole by contacting the side of the header when the tube is inserted in the tube inserting hole.
In this heat exchanger, since an expanded tubular portion is provided, the area of the open end of the tube is larger than the cross-sectional area of the refrigerant path in the tube without the expanded tubular portion. Therefore, rapid reduction and enlargement of the cross-sectional area of the refrigerant path are prevented in the vicinity of the joint of the tube and the header and pressure loss of the refrigerant which flows in and out from the header to the tube is reduced. Since the tube inserting hole is required to be larger than the expanded tubular portion, the guard is located at the end of the tube and seals off the tube inserting hole, so that the refrigerant is prevented from leaking.
According to the present invention, since a portion of the tube without columns is provided at the end of the tube, the opening area of the end of the tube is not reduced by the columns. Therefore, rapid reduction and enlargement of the cross-sectional area of the refrigerant path are further prevented at the vicinity of the joint of the tube and the header, and pressure loss of the refrigerant which flows in and out from the header to the tube is reduced.